Sliding Sleeves have been used in downhole well completions for many years for controlling the flow of wells. These sleeves normally only have two positions, they are either fully open or fully closed and are not adjustable between these two extreme positions. These sleeves have evolved over time from requiring costly manual intervention to remotely operated. The next evolution of these sleeves requires that the flow area of these sleeves to be adjustable. These tools are now generically regarded as downhole chokes. Having the ability to adjust the flow area means that the operators can control the flow of fluids and gasses to and from the reservoir. The primary reason for this requirement is to maximize the efficiency of hydrocarbon recovery from the reservoir and minimize the risks and costs of producing these hydrocarbons.
The indexing mechanism to position the choke valve body in various positions could be subjected to very high forces above those initially envisioned if due to exposure to well fluids and conditions over a period of time the moving parts become much harder to move. Many times the use of available hydraulic pressure at the well head is used with a built in margin to be able to move the moving parts even against resistance caused by binding or particles in the path making the needed movements much more difficult. These designs tend to overpower the moving parts during normal operation in the early goings, when there is not as much resistance to movement between or among the moving parts. These very high forces can cause failure of the parts resulting in a loss in the ability to manipulate the choke into the desired positions.
In the past devices have been created to covert axial motion to rotational motion downhole. This tool was complex, involving a toothed ratchet interacting with a helix on an elongated member. It is illustrated in U.S. Pat. No. 5,584,342. This device was applied to cleaning debris out of pipe. More specific to operation of chokes requiring several positions are U.S. Pat. Nos. 5,826,661 and 6,119,783, which use a sequential application and removal of pressure in conjunctions with slips that allow movement in predetermined amounts, each time the pressure is cycled on and off. This design involved complicated movements and small spring loaded parts that would have been of marginal utility in dealing with large differential pressures which could cause parts to slam together in a manner that could break them or make them stick. Other designs addressed the configuration of the stationary and movable ports, as illustrated in U.S. Pat. No. 6,371,208. The commercial embodiment of this particular design employed a stepper motor operating a rack and pinion to achieve infinitely variable positions for a downhole choke. This system is very complex and expensive to manufacture and operate. Finally, J-slots have long been used in various downhole tools. In a J-slot the pin advances in a slotted track and comes to rest at the closed ends of individual slots so that the relative positions of the two bodies could be determined. The nature of prior art J-slots limited their application to light duty where there was no likelihood of the pin slamming into the end of the slot with great force where is could be damaged or sheared off. A tubing retrievable flow controller model TRFC-H made by Schlumberger uses an indexing system dependent on the location of a ratchet pin and an indexer pin to define multiple positions of a downhole choke.
What is needed is a design that involves simplicity while being able to tolerate large loads caused by high differential pressure applications and the high impact necessarily involved in such operations. The present invention accommodates such severe service by separation of the shifting mechanism from the ultimate positioning mechanism. These and other advantages of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.